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The 7 Li+ 28 Si elastic scattering was studied at near-barrier energies, namely, 8, 8.5, 9, 10, 11, 13, 15, and 16 MeV, with the aim to map the real and imaginary part of the optical potential and therefore probe the threshold anomaly. Angular distributions were measured over a wide angular range of ( lab = 25°to 150°) for the lower energies and of ( lab = 10°to 100°) for the higher energies. The present data, together with previous ones on heavier targets ( 138 Ba and 208 Pb) at near barrier energies, were analyzed by using optical potentials obtained in a double-folding framework. The results were compared with previous measurements of 6 Li on the same targets. It was found that a striking difference occurs between the imaginary potentials of 6 Li and 7 Li, which, respectively, present an increasing and decreasing behavior approaching the barrier from higher to lower energies. On the other hand, this energy variation is not fully reflected to the real part of the potential, as it is described by dispersion relations. The strength of the real potential remains almost constant with a weak declining and uprising trend for the 6 Li and 7 Li, respectively. For a better understanding of our results, continuum-discretized-coupled-channel calculations were also performed and are discussed.

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The production of α particles in the 7 Li + 28 Si reaction was studied at near-barrier energies. Angular distributions were measured at four energies, namely 9, 10, 11, and 13 MeV. The data were treated in a statistical model and DWBA framework to disentangle the degree of competition between direct and compound channels in the reaction and its energy evolution near the barrier. It was found that whereas the compound mechanism is substantial, d transfer and possibly t transfer are the dominant mechanism at near-barrier energies. The influence of the reaction channels on the optical potential threshold anomaly is discussed.